Conventional tufted carpets are made by passing a flexible woven primary backing through a tufting machine having a large array of needles that force the carpet multifilament yarn through the backing where the yarn is restrained by a large array of hooks before the needles are retracted. There may be about 1400 needles across a 12-foot width. The backing must accommodate needle penetration without damage. The backing is then advanced a short distance (about 1/10" for a popular high quality tuft density), and the needles are reinserted through the backing to form the next series of yarn tufts. A large array of cutters may be employed in conjunction with the hooks to cut the tuft loop inserted through the backing to produce a cut-pile carpet. For loop-pile carpets, the tuft loops are not cut. Friction holds the tufts in the backing after the needle has moved to the next position.
However, this friction is insufficient to hold the tufts in place during use as a carpet, so an adhesive is applied in liberal quantities to embed all the filaments in the base of the tuft on the underside of the primary backing (needle entry side). This prevents the pullout of tufts or individual filaments during use. To assist in stabilizing, stiffening, strengthening, and protecting the tuft base from abrasion, a secondary backing is attached to the underside of the tufted primary backing. The secondary backing may be attached by the same adhesive layer or by the application of more adhesive. To save on costs, an inexpensive latex adhesive is most often used. The secondary backing must resist damage during shipping, handling and installation.
One problem with the above-described conventional carpets is their heavy structure. As a result, these carpets can be difficult to install and, after a useful life, are difficult to recycle since many different polymers are used in their construction. Nylon tufts, latex adhesive, polypropylene primary backing, and polypropylene secondary backing are commonly used. These materials are difficult to separate for polymer recovery; latex and nylon polymers are not compatible for recycle. This has resulted in millions of pounds of waste carpet being dumped in landfills each year.
Predominantly nylon ("all-nylon") carpets have been suggested in the past. However, nylon polymer useful for backings in such carpets have a moisture sensitivity that causes as much as 4% to 10% changes in the dimensions of the carpet in response to changes in the humidity from very moist to very dry depending somewhat on the temperature. These problems of moisture and thermal stability have not been adequately addressed in the past, so a carpet with a backing structure that would constantly lay flat in use was not possible. Moisture changes common in residential use can result in large buckles in carpets where the carpet is restrained in movement by contact with walls (in wall-to-wall installations), or frictionally held by heavy furniture or spaced attachment to floors. In particular, moisture variations from near 0% RH to near 100% RH at elevated household temperatures are a concern to the stability of carpets in residential use.
Lightweight carpet constructions have been suggested, but they have relied on the bulk application of adhesives that are messy to handle in the manufacturing process and are difficult to recycle with the nylon polymer commonly used for the yarn tufts. The machines suggested for such lightweight construction were cumbersome to set up and operate as they handled an entire carpet width of materials in a continuous coupled process. They also usually required discrete yarn supplies to feed the process and so required expensive yarn restocking at intervals or frequent stoppages to replace individual bobbins as they randomly ran out.
There is a need for a carpet construction that is lightweight, dimensionally stable in use, and can be recycled easily to produce useful polymers. There is a need for an "all-nylon" carpet that is stable to moisture and temperature changes in use. There is a need for a simple inexpensive method of making such carpets. The present invention provides such carpets.